1. Field of the Invention
The present invention relates to a honeycomb structure capable of supporting catalyst which purifies exhaust gas emitted from an internal combustion engine of motor vehicles.
2. Description of the Related Art
Honeycomb structures have been known and also widely used in exhaust gas purifying systems mounted to an internal combustion engine of a motor vehicle. Such a honeycomb structure supports catalyst therein, namely, on the surface of partition walls forming a plurality of cells in order to purify exhaust gas emitted from the internal combustion engine of a motor vehicle. The honeycomb structure has a structure composed in general of a plurality of cells and a cylindrical outer peripheral wall. Each of the cells formed in the honeycomb structure is surrounded by partition walls. The cells surrounded by the partition walls on a radial cross section of a honeycomb structure have a hexagonal lattice pattern. In the above structure of the honeycomb structure, catalyst is supported on the surfaces of the cells, namely, on the partition walls. Such catalyst is capable of purifying exhaust gas emitted from an internal combustion engine.
Recently, there has been proposed a honeycomb structure having a structure which has thin partition walls in order to reduce the entire weight of the honeycomb structure and a pressure loss. The reduction of the entire weight of the honeycomb structure reduces a heat capacity of the honeycomb structure. Further, the reduction of the heat capacity of the honeycomb structure provides a rapid activation of catalyst supported in the cells, namely, on the surfaces of the partition walls which form the cells.
However, the reduction of the thickness of the partition walls decreases the entire strength of the honeycomb structure. Still further, the reduction of the thickness of the partition walls causes erosion phenomenon in the honeycomb structure. Such erosion phenomenon causes collision of foreign substances contained in exhaust gas with the honeycomb structure in an axial direction of the honeycomb structure. The collision with foreign substance contained in exhaust gas would generate abrasion of and damage to the honeycomb structure, and thereby would decrease the durability of the honeycomb structure. In order to promote the activation of catalyst, when the honeycomb structure is mounted more close to the internal combustion engine of a motor vehicle, erosion phenomenon in the honeycomb structure is more progressed.
In order to solve the above conventional problems, there have been proposed the following various conventional techniques which enhance the strength and durability of a honeycomb structure.
For example, a patent document 1 as a conventional technique, disclosed in Japanese patent laid open publication No. JP 2007-275873, shows a honeycomb structure having a strength reinforcement area. The strength reinforcement area has an approximate straight line area formed in a diameter when observed on a radial cross section of the honeycomb structure. Such a strength reinforcement area increases the strength of the entire honeycomb structure.
Further, a patent document 2 as another conventional technique, disclosed in Japanese patent laid open publication No. JP 2002-326035, shows a honeycomb structure having thick partition walls. These thick partition walls are formed at some of cells in a diameter direction of the honeycomb structure.
However, because the honeycomb structure disclosed in the conventional patent document 1 has strength reinforcement areas. In the strength reinforcement areas, reinforcement cell walls of a large thickness are sequentially formed. However, because a gap between adjacent cells in the reinforcement areas becomes narrow, catalyst is easily clogged between the adjacent cells, and this structure increases a pressure loss. The catalyst clogged in the ells increases the entire weight of the honeycomb structure. Accordingly, the increased entire weight also increases the entire heat capacity of the honeycomb structure. This decreases a rapid activation of the catalyst supported on the surfaces of the partition walls in the honeycomb structure.
Because the honeycomb structure disclosed in the conventional patent document 2 has the partition walls having a large thickness which are formed in a specified part in the entire cells, the honeycomb structure has the same problem caused by the honeycomb structure disclosed in the conventional patent document 1 as previously described.